The present invention generally relates to a balloon catheter for conducting dilatation procedures within the vascular system and in conjunction with a guiding catheter within which the balloon catheter is slidably moved for positioning and treatment. The balloon catheter incorporates an elongated, high-strength cannula as its proximal tube component and has a distal end assembly which incorporates the balloon and which has a flexibility substantially greater than that of the proximal cannula. The proximal cannula and the distal end assembly are joined together by a transition assembly which includes an elongated coil. When negotiating a tight curve during a medical procedure using the catheter system, the coil imparts a force on the guiding catheter which is relatively low so as to avoid unintentional dislodgement of the guiding catheter from its intended position, such as in the atrium of the heart.
In many applications for dilatation catheters, it is important to provide a proximal catheter tube which is relatively stiff and of high strength so that the elongated proximal tube accepts and transmits column forces, as well as torsional forces, from the proximal end of the catheter which remains outside of the body and to the distal end portion of the catheter so that the latter is properly positioned for effecting the dilatation procedure. Proximal elongated tubes such as metal hypotubes have been proposed or used in the past. This type of stiff tubing does not extend the full length of the balloon catheter. In order to maneuver through tight turns and/or constricting passageways, the distal end portion of the catheter must be quite flexible.
While the objective of having a stiff proximal hypotube and a flexible distal portion has been a desirable objective, achieving this objective is complicated by the need for providing a suitable transition between a very stiff elongated member and a very flexible elongated member. It has been found that, when two such diverse stiffness sections interface directly with each other, there is a strong tendency that the catheter will prolapse on itself during movement, especially in the distal direction, of the balloon catheter with respect to the guiding catheter. Among other concerns, this type of action will mean that the balloon catheter does not move consistently smoothly through the guiding catheter. At times, this can result in guiding catheter dislodgement from its desired position within the vascular system of the body, such as in the atrium of the heart.
In the past, catheters of this general type have included a transitional section between a stiff hypotube type of component and a flexible distal end portion of the catheter. A primary component of these types of transitional section approaches is the incorporation of a rigid structure generally at the transition location, whereby the stiffness of the proximal hypotube is gradually reduced as same moves into the flexible distal portion of the catheter. In some known systems, a bridging wire is provided as a distally oriented extension of the hypotube, this being positioned within a transition section between the distal end of the hypotube and the proximal end of the distal end portion of the catheter which contains the balloon.
With approaches such as those generally identified above, the bridge wire or the like creates difficulties when the balloon catheter must be passed through a tightly curved portion of the guiding catheter. There is a strong tendency for the bridge wire to transfer a bending force to the walls of the guiding catheter, due to the stiffness of the bridging wire, which force transfer typically increases when the tightness of the curve which must be navigated increases.
There is accordingly a need for a catheter system having a balloon catheter which will easily navigate tight curves in the distal portion of the guiding catheter and without imparting undue force to the walls of the guiding catheter, which force has been known to result in unintentional dislodgement of the guiding catheter as a result of movement of the balloon catheter therewithin. In addressing this problem, the present invention concentrates on the structure of a transition section between an elongated stiff proximal tube and a flexible distal portion.
Problems to which the present invention are directed can be especially relevant in catheters which incorporate a lumen for guidewire passage which is provided only at the distal end portion of the catheter. Such an overall structure permits the physician to easily and/or rapidly exchange one balloon catheter for another and generally avoids the need for extended length or extendable length guidewires and the problems associated with providing and handling same. Balloon catheter systems of this general type are shown in Yock U.S. Pat. No. 5,061,273 and Leopold U.S. Pat. No. 5,346,505, their subject matter being incorporated hereinto by reference. Generally speaking, by providing a quidewire exit port in a generally distal portion of the catheter, this can intensify the problem of undesired weakness of the catheter caused by stiffness differences between the section of the catheter having the guidewire tube and guidewire and the section of the catheter immediately proximal of the guidewire exit port. There is accordingly a need for an improved transition structure in the vicinity of the guidewire exit port of a balloon catheter having such an easily and/or rapidly exchangeable feature.